Not applicable.
Not applicable.
1. Technical Field of the Invention
The invention relates to, a catheter for the ablation of biological, in particular of animal or human, tissue, including ablation of human myocardial tissue, a method for treating catheters, and an apparatus for carrying out the treatment of catheters.
2. Description of Related Art
One of the main aims in the catheter ablation of myocardial tissue is to interrupt, by lesions of the upper layers of the heart tissue, regions of the conduction system that can have a negative effect on the cardiac action. The success of a treatment depends, however, very substantially on whether the correct depth of lesion was achieved during the ablation. In this case, correct depth of lesion means in essence that the undesired regions disrupting the conduction system are removed, but that no further-reaching injuries are introduced. It is evident that with an excessively small depth of lesion the success of treatment is endangered, whereas in some circumstances an excessively large depth produces very many relatively severe side effects. Since there are vessel walls running in the heart which may not be unnecessarily damaged, and also the tissue to be ablated is frequently only of a limited thickness, in the event of excessively large depths of the lesions it is even possible for lethal accidents to occur because of severed heart walls or heart vessels. An attempt has therefore been made in the case of conventional ablation methods to estimate the optimum depth of lesion by the synchronous recording of ECG signals on the occurrence of success in treatment. However, in this case the irradiated high-frequency energy was exceptionally detrimental to the recording of these signals, and an attempt was undertaken to mitigate such influences by means of appropriate electrical or electronic filters in the downstream equipment. However these attempts had only limited success, or none. Producing the irradiated power led to extremely long treatment times which are in the range of several hours and in this case both subject the patient to substantial stress and are unable to reliably prevent slippage of the ablation catheter. Furthermore, lesion is no longer possible starting from a specific power, since the temperature generated no longer suffices for tissue coagulation.
It is therefore the object of the invention to permit the recording of ECG signals during catheter ablation and, in particular, to improve the quality of the recorded ECG signals to such an extent as to permit medical statements with reference to cardiac action.
This object is achieved by the invention in an exceptionally surprising way with the aid of a catheter for the ablation of biological, in particular of animal or human, tissue, including ablation of human myocardial tissue, said catheter comprising at least one ablation or mapping electrode, wherein the at least one ablation or mapping electrode has a reduced number of electrical interference centers which generate microscopic electric field strength differences or microscopically different reaction capabilities and, wherein the at least one ablation or mapping electrode has a treated surface with a microscopically smoothed surface structure whose microscopic edges or tips have a radius of curvature of more than 10 nm. This objective is also achieved by a method for producing a catheter with improved electrical properties, the method comprising the following steps: providing a catheter which comprises at least one ablation or mapping electrode,-and treating the at least one ablation or mapping electrode its surface, wherein the surface of the at least one ablation or mapping electrode is smoothed at least until structures which have a diameter of less than 10 xcexcm are reduced in number.
The inventor surprisingly followed a completely different path than has previously been the case in the known prior art.
Instead of subjecting the recording equipment to change or an attempt at improvement, the cause of interference in the recording of the ECG signals were reduced or even completely eliminated.
The inventor was the first to find out that the cause of the electrical interference in the ECG recording during simultaneous irradiation of high-frequency energy essentially resides not in the leads to and from the catheter electrodes, not in the electronic recording devices and, in particular, not in their input filters, but in electrical interference centers in the region of the surface of the ablation or mapping electrodes.
This finding was all the more surprising since every investigated ablation catheter with platinum electrodes exhibited such electrical interference centers and, after their reduction or removal, was virtually or completely free from the undesired interference previously described.
In accordance with the invention, in the case of a catheter for the ablation of biological, in particular animal or human, tissue, preferably for the ablation of human myocardial tissue, having at least one ablation or mapping electrode, this at least one ablation or mapping electrode has a reduced number of electrical interference centers. For example, this improves the disturbed ECG recordings illustrated in FIGS. 4, 5 and 7 in such a way that the signals illustrated in FIG. 6 can be obtained.
In a particularly advantageous way, the electrical interference centers which generate electric signals during the output of high-frequency energy to the at least one ablation or mapping electrode and which are essentially arranged on surface regions of the at least one ablation or mapping electrode are reduced in their number, areal extent and/or electrical effect. This results in a removal or electrical deactivation of the influence of these interference centers.
A particularly effective method for achieving the above successes consists in that the at least one ablation or mapping electrode has a mechanically treated surface, since electrical interference centers in the surface can be removed and/or greatly reduced in their effect thereby.
The at least one ablation or mapping electrode preferably has a mechanically treated surface which is treated using a method which smoothes the surface. Prior surface treatments, for example in the case of platinum-iridium catheters, have aimed at enlarging the surface, that is to say precisely not to smooth the surface but to create structures that are rough, having a surface that is larger approximately by the factor 1000; however, the invention proceeds, with surprising success, precisely along the opposite path.
In a particularly preferred and advantageous embodiment, it is provided that the at least one ablation or mapping electrode comprises a noble metal, in particular platinum, whose surface is smoothed, in particular lapped or polished. It has proved in this case to be particularly effective to use a grinding or polishing agent which contains calcium carbonate.
Alternatively or in addition, it can be provided that the ablation or mapping electrode surface is rolled with a smooth roller.
It was frequently to be observed after the above-described treatment that structures of the surface of the at least one ablation or mapping electrode have a rounded surface structure whose edges have a radius of more than approximately 500 nm, preferably of more than 100 nm, but at least more than 10 nm, and it is suspected that these surface changes already cause at least a portion of the reduction in the electrical interference centers or their effects.
It is assumed, moreover, that, owing to the mechanical treatment, peaks in the electric field strength that are present on the surface, for example owing to grain boundaries in the metal, present in crystalline form, are also smoothed or compensated, and that after the treatment according to the invention microscopic differences in the electric field strength or microscopically differing reaction capabilities at the electrode surface are also mitigated or compensated. This mitigates the phenomena occurring during the output of HF energy, which are ascribed without limitation of the generality or the scope of the invention to locally differing ionic mobility, the point being that there is no longer any xe2x80x9crunning onxe2x80x9d by ions or polar molecules which are moved to a greater or lesser extent by different field strengths which would cause the formation of interfering electric potentials or field strengths that are superimposed on the ECG signal as interfering signal. The ions which now move virtually identically at all locations on the surface of the ablation or mapping electrode no longer generate local potential or field strength differences and also no longer disturb the ECG recording.
It is therefore assumed that, when the catheter advantageously comprises a platinum ablation or mapping electrode, the surface of the at least one ablation or mapping electrode is coated or provided at least partially with elementary platinum. It is, however, also within the scope of the invention for such an atomic, essentially non-crystalline or amorphous coating also to be produced, for example, using techniques for coating or plating, for example grinding thin, preferably amorphous films.
It then results in an advantageous way that the surface of the at least one ablation or mapping electrode comprises regions with deposited metal present essentially in an amorphous manner or atomically.